X-Lock VFO Stabiliser

Transcription

1 X-Lock VFO Stabiliser User Manual CONTENTS 1 INTRODUCTION 2 2 PREPARATION 2 3 CIRCUIT DESCRIPTION 3 4 ASSEMBLY 5 5 TESTING 7 6 USER SET UP 8 APPENDIX A Troubleshooting 16 Chestnut Close Culgaith PENRITH Cumbria CA10 1QX UK

2 1 Introduction Thank you for purchasing the Cumbria Designs X-Lock kit. We hope that you enjoy constructing this kit and find many uses for this feature rich design. This manual describes the assembly and operation of the X-Lock kit, even if you are a seasoned constructor, we respectfully ask that you read this manual and familiarise yourself with the instructions and kit contents before commencing construction. If assembled carefully, this unit will provide many years of reliable service. The Cumbria Designs Team 2 Preparation 2.1 Tools We recommend that the following tools are used during assembly and testing; 25W fine tipped soldering 60/40 Rosin cored solder 5 or smaller diagonal side cutters Small pointed nosed pliers Solder sucker (just in case!) Multimeter 2.2 Conventions The following symbols are used within the assembly instructions to draw attention to critical steps such as component orientation and anti-static precautions. The associated narrative describes the action required.! Critical Step Static Sensitive 2.3 Assembly The production of a successful finished working kit is dependent upon careful component handling, careful placement and good soldering! Don t be tempted to rush the construction, even though this is a relatively simple kit, a wrongly placed component can provide hours of frustrating fault finding. Also, as this kit uses a double sided Printed Circuit Board (PCB) with through plating, removal of a wrongly soldered part can be difficult. Follow the assembly instructions carefully to avoid mistakes. 2.4 Component Identification All parts carry a coded identity to describe their values. It is important to be able to recognise these during assembly. Capacitors have their value printed numerically, e.g. 104 = 100nF, 103 = 10nF etc. Resistors have their values represented by coloured bands this is a frequent source of confusion! To simplify component identification, the parts list carries the identities of each component as it appears on the device. For resistors the colour coding is given. This should be referred to during assembly to ensure the right parts are placed in their respective positions on the PCB. 2.5 Component Leads Many of the passive components will require their leads to be formed to align with the holes on the PCB. This mainly applies to the axial parts such as resistors and diodes. Forming X-Lock Version 9.0 PCB 2.0 Page 2 of 14

3 component leads is easily done with a pair of pointed nose pliers and using the hole spacing on the PCB as a measure. Alternatively, small formers made from scrap off cuts of Vero board etc make ideal templates that produce consistent results. Some parts, such as variable resistors, have preformed leads designed for machine assembly. These will require straightening to align with the board layout. Again, a pair of pointed nose pliers should be used to carefully flatten the factory performing to produce straight leads. 2.6 Soldering Before applying solder check carefully that the component you have placed is in the right position! This is a through plated double sided board. Whilst some of the pads are very small, the area presented by the through plating is more than adequate to allow good solder flow to form mechanically strong good electrical joints. These can be difficult to undo, please double check! The majority of problems are likely to be caused by soldering faults. These can sometimes be difficult to find. Here are some basic golden rules that will help you to avoid poor solder joints; Clean Iron Make sure your soldering iron tip is in good condition and tinned. A small moistened pad for cleaning tips, regularly used to wipe off excess solder and flux, will ensure that your iron performs well. Remember to tin the iron immediately after each wipe. Clean Leads and Pads All of the component leads and PCB pads in this kit are pre-tinned and should not need cleaning before soldering. Please ensure that parts are handled so as to avoid contamination with grease or fingerprints. Soldering This is the bit that can trip up even experienced constructors. For the solder to fuse with the surfaces to be joined it is necessary for them to be hot but not so hot as to damage the parts! It s a simple as 1-2-3; 1. Place the tip of the iron against the joint, hold it there briefly to bring the metal surfaces up to temperature. 2. Apply the solder allowing it to flow smoothly onto the surfaces. 3. Remove the iron and inspect the new joint. The finished joint should have a smooth shiny coating of solder. If the joint is dull grey or has formed a spherical blob, apply the iron to the joint, remove the old solder with a solder sucker and re-solder. 3 Circuit Description 3.1 General The X-Lock is a micro-controller based frequency stabiliser designed as an easily applied add-on to enhance the frequency stability of existing free running variable frequency oscillators (VFOs). This compact module will accept an input signal with a range of a few tens of khz to over 50MHz and produce a variable correction voltage to drive a simple drift compensation circuit fitted to the host oscillator. To minimise the risk of introducing digital noise to the host oscillator, the analogue section of the X-Lock operates from its own regulated supply and is optically coupled to the digital control circuitry. A tri-colour LED provides operational and diagnostic information of the X-Lock status. In common with all types of frequency stabilisers, the X-Lock will make a good VFO even better, however it will not make a badly designed or constructed VFO into a good one! X-Lock Version 9.0 PCB 2.0 Page 3 of 14

4 There are three two pin connectors on the X-Lock; RF Input, Control Voltage output and the nominal 12V DC supply. A three way connector is provided to allow optional remote connection of the tri-colour LED. 3.2 Theory of Operation The Cumbria Designs X-Lock is a derivative of the Huff-Puff stabiliser system devised by the late Klaus Spaargaren PA0KSB in the 1970 s. This and other similar frequency control systems operate by comparing the frequency of the controlled oscillator with a crystal reference (hence X-Lock = Xtal-lock), to produce a correction signal. This is used adjust the frequency of the oscillator to compensate for any measured drift. The frequency control of the host oscillator is usually realised by a varactor (varicap) diode although some systems use an inductive device with variable permeability or even motor controlled capacitors. The X- Lock is design to operate with a varactor. The X-Lock operates by measuring the frequency of the host oscillator by the gate/counter method. This is the same technique used by most digital frequency counters. At the heart of the X-Lock is a 16F628 processor (IC3) which performs all of the measurement and control operations. The input signal is buffered by Q1 and amplified by Q2 before being presented to the input of the processor on pin RB6. The gate circuit is internal to the processor and operates over a 100mSec period to provide a count resolution of 10Hz. The value of each measurement is compared with the previous and if the difference is equal to or less than 40Hz, the 16F628 processor will generate a correction signal. This takes the form of a variable duration control pulse on either the Up or Down signal lines from the processor. These drive LED s within the Opto-coupler, IC4, to switch on or off their associated transistors either charging or discharging the voltage stored in the loop filter R9, C11 and C15. The time constant of the loop filter is very long resulting in a slow rate of change of the control voltage. To ensure that the control voltage starts at centre rail, a reset switch formed by FET Q3 is enabled by the processor on power on. This ensures that C11 and C15 are fully discharged. Following discharge, once Q3 is turned off, the capacitors (because they are the same value) recharge via R5 to restore a centre rail output voltage. In the unlikely event that the loop control voltage becomes saturated, say after a prolonged period of operation, the control voltage can be set to centre again by briefly powering the X-Lock on and off to operate the Q3 reset switch. The host VFO will need to be retuned following a reset. A rail to rail operational amplifier IC5, buffers the filter, providing a low impedance source for the control voltage to drive the external compensation varactor. Whilst the varactor circuit will exhibit a very high impedance at DC, the low impedance of the operational amplifier output stage reduces the effects of stray voltages on the control voltage line. A simple RC filter (R10 and C16), decouples the control signal at the point where it leaves the X-Lock PCB. There are two voltage regulators on the X-Lock PCB. IC2 provides the +5V supply for the 16F628 and the input amplifier, IC1 provides +8V supply for the loop filter and output amplifier. The use of separate regulated supplies provides good isolation between the digital and analogue stages and offers a wide operating range for the control voltage reducing the possibility of loop saturation. A 1N4004 power diode, 100K resistor and 22pF and 68pF capacitors are included with the X-Lock kit. These are intended to be configured as a X-Lock Version 9.0 PCB 2.0 Page 4 of 14

5 varactor correction circuit shown in fig.1. This circuit should be suitable for most applications up to about 15MHz. Above this frequency the value of the coupling capacitor may need to be reduced considerably to prevent over correction. 4 Assembly The following assembly sequence is recommended. This allows most of the smaller parts to be held in place with the board turned over whilst soldering the underside. All components are mounted on the top (silk screen) side of the board. 4.1 Fixed Resistors (Broad tolerance band shown in capitals) 100R R4, R6 Brown, Black, Black, (BROWN) 390R R7, R12, R13, R15 Orange, White, Black, Black, (BROWN) 470R R2, R8, R16 Yellow, Mauve, Black, Black, (BROWN) 1K R3, R5, R17 Brown, Black, Brown, (BROWN) 10K R1, R10, R18 Brown, Black,Black, Red, (BROWN) 100K R11 Brown, Black, Black, Orange, (BROWN) 2M2 R14 Red, Red, Black, Yellow, (BROWN) 4.2 IC Sockets! Ensure correct orientation! Match index cut out on socket to board printing. Tip; solder one pin only then check positioning before continuing. Heat solder and reposition if necessary. a) Fit the 18 pin microcontroller socket for IC3 b) Fit 8 pin sockets for IC4, IC5 4.3 SIL Socket (For R9) Cut off the thin sections of two centre pins in the 4 way SIL strip to allow it to be fitted flush into the R9 position. Solder the SIL strip in place. Trim and fold the leads of R9 such that it plugs neatly into the SIL socket. 390K R9 Orange, White, Black, Orange, (BROWN) 4.4 Crystal Fit X1, the 20MHz crystal. This is heat sensitive and is easily damaged if overheated. It is recommended that a gap of about 2mm is left between the crystal and the PCB. This will provide a little extra thermal isolation during soldering. 4.5 Ceramic Capacitors Suggested Installation order; 22pF C5, C6 22J 10nF C2, C8, C9, C10, C13, C14, C16, C nF C7 104 X-Lock Version 9.0 PCB 2.0 Page 5 of 14

6 4.6 Transistors! Polarity conscious components. Make sure that orientation is correct. The J310 and 2N7000 are Static sensitive parts. Discharge yourself to ground before handling. Avoid wearing static generating clothing (e.g. wool, man made fibres etc) during assembly. a) Fit JFET Q1 J310 b) Fit Bipolar transistor Q2 MPSH-10 c) Fit FET Q3 2N7000! 4.7 Regulators Polarity conscious components. Make sure that orientation is correct. When installing the two T092 Voltage regulators, ensure that their orientation matches that shown on the silk screen. a) Fit 5V regulator IC2 78L05 b) Fit 8V regulator IC1 78L Electrolytic Capacitors! C9 and C11 are polarised Capacitors, observe the polarity shown by the silk screen. 10uF 100uF C1, C4, C12 C3, C11, C Connectors Recommended Pin Header Connector orientation is with rear locking tab facing into the centre of the board. A three way header is provided for the LED to allow it to be remotely fited to a front panel if required. a.) b.) Fit the 3 two pin headers PWR, RF, VAR If you wish to extend the Tri-Colour LED, fit the three way LED header LED The Tri-colour LED has three leads. The centre lead is the cathode and the two outer leads are anodes for the red and green LEDs. The shorter of the outer leads is the red LED anode. The Tri-colour LED is connected with the short lead (red anode) nearest the crystal X1. The LED may be mounted directly on the PCB or connected via the supplied three way header if remote viewing is required Semiconductors Static sensitive parts. Discharge yourself to ground before handling. Avoid wearing static generating clothing (e.g. wool, man made fibres etc) during assembly. X-Lock Version 9.0 PCB 2.0 Page 6 of 14

7 ! Orientation is critical. Observe correct alignment of IC pins which will need to be gently formed for correct alignment before insertion into sockets. IC pins can be pushed inwards by placing the device on its side on a firm surface, and gently pressing the body down against the pins. When inserting parts, take care to check pin alignment. Fit IC3 PIC16F628A Processor (18 pin DIL) Fit IC4 TIL192 Dual opto-coupler (8 pin DIL, white body) Fit IC5 TS951 Operational Amplifier (8 pin DIL) 4.12 Connector Assemblies Connector shells and pins are supplied to allow connection of power and signal lines to the X-Lock. The use of good quality, colour coded, heat resistant, multi stranded wire is recommended. To avoid accidents, a colour code convention should be chosen to represent function, e.g. Red +ve supply, Black ground, striped colours controls etc. The connector assemblies comprise of two components; the shell and the pins. To terminate a conductor first strip back about 2mm of insulation and tin the exposed wire. Place the tinned end of the wire into a pin such that the tinned wire sits inside the inner pair of tabs and the insulation sits within the outer tabs. With small pointed nose pliers carefully compress the outer tabs onto the insulation to hold the wire. Repeat this with the inner tabs to grip the exposed conductor. Very carefully solder the exposed conductor in place taking care not to allow solder to flow onto the locking tab. Finally, insert the pin into the shell with the small locking tab orientated to the face of the shell with the small cut outs. Push home until the locking tab snaps into the cut out. Should you need to remove a pin, gently press the locking tab in with a small screwdriver or the end of a pair of pointed nose pliers. The pin will be released and can be pulled out of the shell. Assembly complete, well done! Now carefully check your work for dry joints and bridges before moving on to testing. 5 TESTING Before connecting the X-Lock to your power supply for the first time, carry out these simple checks just to be safe! 5.1 Basic Electrical Tests Volt Input With a multimeter set to resistance, place the Red meter lead onto +12v and the Black to Ground and check for a high resistance. Note that due to C11 charging the reading will show change, providing there is not a short circuit then all is well and +8 Volt Rails Carry out the resistance test on the output side of the regulators (IC1 and IC2) to check the integrity of the regulated rails. Due to the circuitry of the X-Lock a much lower resistance will be measured, the reading will depend upon the characteristics of the multi-meter but typically should be around 250 Ohms. X-Lock Version 9.0 PCB 2.0 Page 7 of 14

8 5.2 Powering Up Power With no controls set, connect a +12 volt supply to the X-Lock. Double check the polarity, take a deep breath and switch on. The status LED will sequence through Red, Amber and Green and then flash Red on and off indicating that there is no signal input RF Checks Connect a signal source of around 500mV peak to peak or greater between the RF input pin and ground, the status LED should stop flashing Red. If it doesn t, check the connection to the oscillator and the signal level. At higher frequencies, more drive may be necessary. If the signal source is stable enough, the LED may illuminate Green indicating that the drift rate between measurements is low. This concludes the unit testing. 6 USER SET UP 6.1 Installation Install the X-Lock as close as possible to the VFO that it will work with. Keep all signal leads as short as possible to minimise any unwanted radiation or pick up. The X-Lock requires a smoothed DC supply in the range +10V to +16V, supply voltages greater than +16V should be avoided to prevent over heating of the regulators. 6.2 Connection to a VFO The RF input should be taken from the output of the buffer stage to avoid loading the VFO. This will typically be a low to medium impedance source which should be capable to Control Voltage from X-Lock (VAR) 10nF Ceramic Coupling Capacitor (See Text) 100K To VFO tuned circuit Varactor Diode (1N4004) developing 500mV peak to peak or greater across the X- Lock RF input without a significant reduction in level. Cathode (Control Voltage) Anode (Ground) The control voltage output (VAR) of the X- 1N4004 Lock is used to drive a varactor in the VFO tuned circuit. A Fig.1 VFO Connection 1N4004 diode, 100K resistor, 10nF and 68pF and 22pF capacitors are included in the kit to form the varactor circuit. Whilst the 68pF or 22pF capacitors should be satisfactory for many applications, it may be necessary to reduce this value significantly, particularly for high VFO frequencies or where the capacitor is connected directly across the VFO tuned circuit. In these instances the frequency control range may be excessive, possibly up to 100kHz or more, resulting in poor lock or high levels of ripple. For best results it is recommended that the coupling capacitor value is X-Lock Version 9.0 PCB 2.0 Page 8 of 14

9 chosen to give around 20kHz of frequency change for a control voltage range of 0v to +12v. (Test the varactor control range without the X-Lock connected). Alternatively it may be possible to find a connection point in the VFO circuit where either the 22pF or 68pF capacitor will give a satisfactory tuning range. This might be an existing tap on the inductor or across the lower feedback capacitor in the case of a Colpitts oscillator. The circuit configuration is shown in Fig.1, all component leads on the VFO side of the 100K resistor should be kept as short as possible to offer best mechanical stability. Be careful to confirm that the voltages at the point of connection in the VFO do not exceed 50v DC. The AC component should be no greater than 5v p-p. 6.3 Time Constant The rate of change of the control voltage is set by the value of the R9, C11 and C15 time constant. To allow this to be changed, R9 is mounted as a push fit into a strip of SIL socket. The 390K resistor provided should work well in most applications but can be easily changed by plugging a new value into the SIL socket. The optimum value will provide good stabilisation with no warble caused by changes in the correction signal. If the 10Hz correction signals can be heard as a warbling effect on a received signal then try increasing R9 or alternatively reduce the value of the coupling capacitor in the varactor circuit to reduce the tuning range of the varactor. 6.4 Operation with VFO Initialisation On switch on the X-Lock will run through an initialisation check (indicated by the red/amber/green phase of the tri-colour status LED) and then commence measurement the host VFO frequency. Once the VFO switch on drift has fallen below 40Hz/sec, the X-Lock will apply correction control signified by the status LED changing from red to green. Depending upon the VFO warm up characteristics, lock may be intermittent during the first minute or two of operation Tuning When adjust the VFO tuning the X-Lock will halt correction and hold the varactor control voltage at the current value. The status LED will turn red indicating an unlocked state. Once tuning is stopped, the X-Lock will wait for 2 seconds before re-applying lock. This reduces control voltage creep during fine tuning RIT An innovative feature of the X-Lock (version 2 upwards) is the ability to detect rapid frequency changes associated with RIT operation in a transceiver. Once RIT operation has been identified, the X-Lock stores the two frequencies used for transmit and receive and recalls these after each frequency excursion. Providing that the frequency shift is consistent during transmit and receive changes, the X-Lock will provide a fast lock with greatly reduced long term control voltage creep when compared to a non RIT compensated stabilisation system. X-Lock Version 9.0 PCB 2.0 Page 9 of 14

10 6.4.4 Changing the Post Tuning Delay Following detection of tuning, the X-Lock applies a delay before re-engaging the frequency correction process. This allows time to make slow or fine manual tuning adjustments to the VFO without the X-Lock attempting to compensate for what it may see as drift. This Hold Off Delay is set at 2 seconds but for some applications or for personal preference, other delay periods may be desirable. The facility to change the hold off delay to periods of 1 to 15 seconds is provided within the X-Lock software. The Hold Off Delay is changed as follows; a) With the X-Lock powered up disconnect the VFO input. The status LED will flash red once every second indicating no signal input. b) Using a short piece of wire, ground pin 4 of the PIC. The status LED will now flash amber once every second indicating that a new Hold Off Delay is being entered. Each amber flash represents a 1 second increment in the new Hold Off Delay. c) Once the required number of seconds has been reached, remove the ground condition from pin 4. The status LED will now revert to red flashes indicating a loss of input signal. d) Restore the VFO input. The new Hold Off Delay has been saved and is now active. Note. Once the limit of 15 seconds is reached, if the ground condition is still applied to pin 4 the status LED will flash red. Appendix A Troubleshooting The following checks may help in identifying the cause of operational problems. Area Symptoms Actions LED LED regularly flashes RED Input level too low or absent, check connection to VFO and drive level. Power No Lock Time Constant LED permanently RED or LED flickers RED/GREEN. Received signals sound clean. Power applied but unit doesn t work. Little or no current drawn. LED goes through initialisation sequence but there is no control voltage output. VFO jitters causing warbling modulation on received signals. LED Flickers GREEN/RED. VFO sounds clean but still drifts. LED Flickers. X-Lock LED shows lock and VFO is stable but warbling evident on received signals. Input OK but VFO drifting greater than 40Hz/second. (Normal during VFO initial warm up). Check varactor circuit installed correctly, check control voltage present at varactor circuit input. Check Power Supply polarity. Check +12V on inputs to Regulators. Check Regulator Ground continuity Check +8V regulator for input and output, confirm correct orientation. Are IC4 and IC5 inserted correctly? Check soldering of IC4 and IC5 pins Varactor is over compensating pulling VFO out of lock range. Reduce coupling capacitor value and/or replace Red LED with a varactor diode with a lower capacitance range. VFO not stable enough. Check design. Time constant too high, reduce plug in resistor R9. Increase time constant by changing value of plug in resistor R9. X-Lock Version 9.0 PCB 2.0 Page 10 of 14

11 X-Lock Schematic X-Lock Version 9.0 PCB 2.0 Page 11 of 14

12 X-Lock Component Overlay The Assembled Kit X-Lock Version 9.0 PCB 2.0 Page 12 of 14

13 X-LOCK PCB VERSION 2.0 PARTS LIST Resistors 2 100R R4, R R R7, R12, R13, R R R2, R8, R16 3 1K R3, R5, R K R1, R10, R K R K R9 1 2M2 R14 Capacitors 2 22pF Ceramic Capacitor C5, C6 8 10nF Ceramic Capacitor C2, C8, C9, C10, C13, C14, C16, C nF Ceramic Capacitor C7 3 10uF Electrolytic Capacitor C1, C4, C uF Electrolytic Capacitor C3, C11, C15 Semiconductors Q1 J310 JFET Q2 MPSH10 NPN transistor Q3 2N7000 FET IC1 78L08 8v T092 Regulator IC2 78L05 8v T092 Regulator IC3 PIC16F628A Microcontroller IC4 TLP521 Dual Optocoupler IC5 TS951 Operational Amplifier LED Tri-colour LED Crystal X1 20MHz Connectors and IC Sockets 1 3 Way Pin Header JP1 1 3 way Shell 3 2 Way Pin Header PWR, RF, VAR 3 2 Way Shells 9 Crimp Pins 1 18 Pin DIL Socket 2 8 Pin DIL Sockets PCB X-Lock v2.0 External VFO Parts 1 1N4004 Diode 1 100K Resistor 1 22pF Ceramic Capacitor 1 68pF Ceramic Capacitor 1 10nF Ceramic Capacitor X-Lock Version 9.0 PCB 2.0 Page 13 of 14

14 NOTES X-Lock Version 9.0 PCB 2.0 Page 14 of 14